[Tim Wetzel]

Thanks, Edwin. I think I’ve cracked it.

I’m not a tech guy, but here goes: Since .webm is so highly compressed, as I unfolded it, it just grew bigger and bigger, like one of those pellets you drop in water and grows into a dinosaur. The key was changing settings on MPEG StreamClip.

Here’s the steps I took:
Converted .WEBM to .H264 mp4 in iDealshare VideoGo
Converted .mp4 to .mov in MPEG-Streamclip

Settings: ProRes 422, 100%, Sound unscaled, and here’s the key, video unscaled (it was 1920×1080), but set the frame rate (I used 29.97), deselected everything under ‘deselect for progressive movies,’ then made the movie.

It’s still big, but not outrageous, and very good quality.

[Tim Wetzel]

Right? It’s weird.

I’m using MPEG Streamclip, 422ProRes, 100%, unscaled, everything else is default (though it doesn’t matter if I change it to 720).
I have also tried through iDealshare VideoGo. Same result.
The only thing I can figure is, since .webm is for HTML, the pixel count doesn’t line up to movie formats. Then, when it converts, it’s trying to keep the original resolution which is not actually equivalent to .mov, but much, much denser as perceived through conversion.

[Tim Wetzel]

Thanks for the response, Edwin.

The raw footage is over twenty minutes long, .webm. It’s 1920×1080. I have been converting a 30 second piece to ProRes422, 1280×720 to figure out a sensible workflow. I just did a 30 second conversion as described. It took 18 minutes and the file size is almost 10 GB for 30 seconds!

.webm is not a format I’ve used before. The entire source .webm file is only 51.1 MB. I can find plenty of stuff to create it, but very little to un-create it! 🙂

I know I’m just missing something here…